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In order to clarify the effects of small addition of silicon content on the grain size refinement in ferrite-martensite duplex steel, the average grain size, distribution of martensite phase and mechanical properties of this steel were investigated in this work. The results obtained are as follows; 1. The average grain size of the duplex steel containing Si below 0.2 wt% decreases with increasing Si content but the duplex steels exhibit different effects of grain size refinement depending upon the types of heat treatment cycle. 2. The duplex steel containing 0.1 wt% Si has the finest grain size (about 1 ㎛), and exhibits excellent mechanical properties (260 MPa yield strength, 640 MPa tensile strength, 28% total elongation and 25% uniform elongation). 3. The finer the starting structure, the finer the grain size of the duplex steel. 4. The grain size of the duplex steel decreases with increasing intercritical annealing temperature for a given holding time.

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In this study, a low temperature sintering proces at 1000-1300℃ in CO₂ atmosphere was employed, and three green pellets with O/U ratio of 2.17, 2.19 and 2.49 were used to investigate the effect of the O/U ratio on the microstructure and density of sintered UO₂ pellets. As the O/U ratio of green pellets increased, the quantity of fine grain (i.e., smaller than 2㎛ in diameter) decreased, and the sintered density decreased. When green pellets with O/U ratio of 2.49 was sintered, the monomodal microstructure, which is mainly consisted of uniform and coarse grains (i.e., larger than 30㎛ in diameter), was obtained.

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A study has been made of a X-ray method for measuring the volume fractions of component phases in α+β` brass sheets and α+ β` Pb brass rods having textures. Taking into account only one reflection intensity from each phase leads to serious errors in results regardless of the textures. Five or six lower index reflections from each phase have to be taken into account to achieve satisfactory results.

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Electrical resistivity and Hall coefficient of Co-early transition metal (ETM; Zr, Nb and Mo) thin film alloys were studied. Electrical resistivity was linearly increased with increasing solute concentration in spite of the structural difference. The increasing rate of electrical resistivity per 1 at % of solute was about 15,10 and 5μΩ㎝ for Nb, Zr and Mo, respectively. Electrical resistivity slightly decreased with increase of the input power and sputtering time and rapidly increased with increase of Ar pressure. From the relation between electrical resistivity and Hall coefficient, it was considered that the Hall effect in Co-Zr amorphous thin film was controlled by side-jump mechanism.

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Magnetic measurements on the rapidly solidified Fe Al_(1-x)Cu_x series (x = 0.05-0.40) have been made at temperatures from 77˚K up to 700˚K, and compared with those of the annealed specimens. It was found that ferromagnetis appealed in the alloys with x≥0.30, and the alloys with x≤0.25 remained paramagnetic down to 77˚K. In the ferromagnetic region, magnetization increarses as x increases and so does the Curie point. Rapidly solidified specimens show higher magnetizations and Curie temperatures than those of the annealed. X-ray diffraction data revealed that both specimens, rapidly solidified or annealed, were single-phased in CsCl(B₂) structure with a virtually constant lattice parameter of 2.91A. Rapidly solidified alloys, however, exhibited some extent of disorder in the site occupancies of Al atoms and Fe atoms. The results were analized in terms of the local environmental effect of magnetic atoms.

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The effects of gas atomization variables on the particle size distribution and particle shape of Al alloys were studied with the self-manufactued high pressure gas atomizer at the range of melt flow rate (Mm) of 1.8-8.0 ㎏/min and gas flow rate (㎎) of 1.7-3.0 ㎏/min. In these ranges, powders of mass mean diameter of 40-100㎛, and geometric standard deviation of 1.2-2.8 were obtained. The ratio of ㎎/Mn seemed to be the dominant factor determining the particle size distribution by affecting the prefilming behavior of the melt: as the ratio of ㎎/Mm increased, the melt prefilm seemed to become thinner, and finer particles were produced. Liquid state volume contraction, oxidation and collision between powders were the main factors determining the powder shape. The cooling rate of 270 mesh powders manufactured in this study was estimated to exceed 5×10⁴K/sec.

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Microstructures and texture of a 90-10 brass have been investigated to characterize the deformation mechanism during rolling reduction from 60 to 90% utilizing X-ray diffraction technique and electron microscopy. Two types of microstructure have been identified. One is a substructure consisted of thin deformation twins and shear bands. The other is a substructure consisted of microbands and shear bands. It is found that the overall deformation occurs in a series of overlapping stages, in each of which a single mechanism predominates. As rolling reduction increases, transitions of texture from a copper-type to a brass-type (at 80% reduction) and to the Goss-type (at 90% reduction) are observed. The first transition depends upon mechanical twinning, while the second one on shear band formation.

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A detailed examination was carried out to clarify the effect of Cu on precipitation hardening of Fe-Ni-Al alloy by varying the amount of Cu and measuring the yield strength, hardness, and electric resistivity. Electolytically extracted residue was also analysed by transmission electron microscope. The absolute strength of Fe-XCu-3Ni-1Al alloy after aging at 500℃ increased and rapidly reached maximum strength with increasing Cu wt.% due to the increased Ni Al phase precipitated at intragranula. Intergranular precipitation of ε-Cu during aging increased with increasing Cu wt.% in Fe-XCu-3Ni-1Al alloy. It was found that ε-Cu precipitation promoted precipitation of the Ni Al phase by in-situ nucleation. The major strengthening mechanism during aging at 500℃ in Fe-XCu-3Ni-1Al alloy was attributed to the fine Ni Al-precipitates coherent with the ferrite matrix.

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